They're simple, social, and entirely made for mobile, all of which might explain the explosive growth of standalone messaging apps even as Facebook offers a free way to chat on smartphones.

One of the biggies, Kik says that it now has more than 50 million users and that people -- mostly young people -- are signing up at a rate of 200,000 a day. That's twice the rate that Kik claimed when it last released stats. Just last November, the app claimed 30 million users and said that 100,000 people were signing up each day.

"It's just crazy," said Ted Livingston, the 25-year-old founder and CEO of Kik. "This is all about the network effect."

Along with boasting new stats, Kik today is releasing a new version of its app for both Android and iOS. The big advance, said Livingston, is that Kik is adding in-app push notifications, which is a first for apps built with HTML5.

Last November, Kik came out of an 18-month stretch of development to unveil Kik Cards. It's a slick way to share content -- YouTube videos, say, or images you grab off the Web -- that doesn't interfere with Kik's simple interface. With Kik Cards, you swipe the main conversation screen to the right (there's a tiny handle) to reveal cards.

Today, Kik is adding a Card, called Memes, that lets users easily take a picture of a meme and share it. All told, Kik says that it's had 25 million installs of individual Kik Cards. Kik is also changing the way the Cards are organized on the app. Now, Cards will sort themselves by which ones you last used -- something Livingston said works better as Kik adds more Cards.

Facebook, of course, is working hard to keep people using its Messaging app, but younger people are often using apps like Kik instead. That's in part because they have become social networks in themselves -- places where friends can share content, chat in groups in a way that feels more intimate than Facebook.

"When someone sends me a message on Facebook," said Livingston, "it feels like an e-mail. On Kik, it feels like texting."

About the author

Paul Sloan is editor in chief of CNET News. Before joining CNET, he had been a San Francisco-based correspondent for Fortune magazine, an editor at large for Business 2.0 magazine, and a senior producer for CNN. When his fingers aren't on a keyboard, they're usually on a guitar. Email him here.
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